1. Field of the Invention
The invention refers to a bracket for producing tooth movement in the treatment of dental malocclusions.
2. Description of the Related Art
Orthodontic brackets comprising a base plate for attachment to the crown of a tooth and comprising a structure attached to the base plate, elevated over the base plate, said structure having at least one slot for receiving an archwire are generally known and described e.g. in U.S. Pat. No. 5,562,444 (Heiser et al.), U.S. Pat. No. 5,074,783 (Reher), U.S. Pat. No. 5,022,854 (Broughton) and U.S. Pat. No. 4,415,330 (Daisley et al.), the contents thereof are incorporated in this specification by reference.
For the orthodontic treatment of a patient having malposed teeth, the brackets of a complete set of brackets are attached in predetermined positions at the crowns of the teeth of the patient, e.g. by the aid of a cement or adhesive, and subsequently, a common archedly extending archwire is inserted into the archwire slots in the structures of the brackets of a jaw so that the brackets are lined up on the archwire like pearls on a string, see e.g. FIG. 1 in U.S. Pat. No. 4,283,908 (Kurz). The archwire is secured in the slots of the brackets by means of ligatures or my means of closing springs, see e.g. the U.S. Pat. No. 5,562,444 (Heiser et al.).
The brackets are mounted on the crowns of the teeth in a manner that they each have a predetermined orientation with respect to the tooth, see e.g. the U.S. Pat. No. 5,022,854 (Broughton), according to which imaginary prolongation lines of the lateral edges, i.e. sight lines, of the specially formed base plate of the bracket intersect in the tip of the root of the respective tooth. According to the malposition of the teeth of the patient to be overcome, the archwire inserted into the bracket slots at the beginning of the orthodontic treatment has an irregular, more or less waved or angled extension.
Caused by the resiliency of the archwire, the archwire exerts a torque onto the brackets and consequently onto the teeth, which, due to the durability of its influence finally causes the teeth to yield and gradually move to a proper position determined by the orthodontist so that at the end of the orthodontic treatment the archwire connecting the brackets substantially extends in a straight line apart from its arched extension following the arched shape of the jaw.
If the malpositions of the teeth are too great, a relatively thin archwire is sufficient at the beginning of the treatment to cause the required torque at the teeth. An archwire that is too thick would cause an excessive torque. The more the tooth position approaches the proper position, the thicker the archwire must be to exert the torque necessary for moving the teeth. Thus, the archwires are exchanged several times during an orthodontic treatment. However, the brackets are not exchanged. The latter are dimensioned such that the thickest possible archwire can still be received in archwire slots of the brackets.
The movement tolerance or malposition tolerance, that can be comprised by means of an orthodontic treatment of this kind is approximately 15.degree. angle of rotation at the tooth. However, a thin archwire, as it is used at the beginning of the treatment, has a clearance of movement within the slot of each bracket of approximately 8.degree., so that under certain circumstances an effective angle of rotation of 7.degree. only remains about which the tooth can be rotated by means of said thin archwire. This was taken into account and compensated for by an early exchange of the thin archwire against a thicker one.
The frequent exchange of the archwires is a nuisance for the patient and requires a lot of time, and it is also very expensive because of the medical treatment.